The present invention relates generally to scroll compressors and more specifically to a liquid injection system for preventing overheating of the scroll compressor.
Scroll compressors are becoming increasingly popular due to their capability for extremely high operating efficiency as compared to prior reciprocating, rotary and screw compressors. However, one problem such scroll compressors have in common with these other types of compressors is the need to avoid excessive heating of the compressor during high load operation.
In order to overcome this problem, liquid injection systems have been previously developed for scroll compressors. In one such prior system a thermostat is placed on the outer shell in an area adjacent the discharge from the compression chambers. The thermostat serves to control the injection of liquid into the compression chambers at a point intermediate the suction inlet and discharg openings. The compressor also includes separate thermally responsive means to deenergize the compressor in response to excessive temperature.
While this arrangement does serve to help in preventing overheating of the compressor, the placement of the thermostat on the shell reduces the accuracy thereof in that the actual temperature sensed by the thermostat will vary depending upon ambient conditions. Thus, for example, cool ambient conditions may result in a sensed discharge temperature lower than the actual thus delaying the actuation of the injection system. Also high ambient conditions may result in premature actuation of the injection system or excessive amounts of liquid being injected.
The present invention, however, provides a unique fluid injection system including a control system therefor which is operative in direct response to excessive discharge temperature to inject condensed liquid into the compressor so as to thereby avoid overheating. In the event the injection of liquid into the compressor fails to reduce or prevent further increase in the discharge gas temperature, further means are provided responsive thereto to deenergize the compressor.
In one form, the liquid injection control system incorporates a pair of thermostats positioned within a common well or housing extending into this discharge chamber, one of which serves to control valve means for injecting liquid into the suction chamber while the other is responsive to further increases in discharge temperature to deenergize the compressor. In another embodiment, a single thermostat having two separate trip points is utilized to control both liquid injection and compressor deenergization. In a still further embodiment, a thermal transducer is utilized which operates to transmit a signal indicative of discharge temperature to a suitable microprocessor which microprocessor operates to control both liquid injection and compressor deenergization.
Thus, the liquid injection system of the present invention provides dual protection against possibly damaging overheating of the compressor. Further, because the discharge gas temperature is sensed at or immediately adjacent its entry into the discharge muffler, the present invention assures greater accuracy in the control of the amount of liquid being injected as well as more response time.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.